Numerical controls are used in a variety of types of machines and must therefore be adaptable to the individual machine as best as possible.
A numerical control must be able to actuate machines which have a plurality of movable axes. For example, machine tools for machining in five axes are quite common, for which two pivot or angle axes are provided in addition to the three linear axes, in order to be able to process a workpiece in a single clamping from all sides.
For each drive of such a machine, the control must have a separate drive controller, whose task consists of moving the particular axis according to a parts program.
For this purpose the so-called interpolator outputs a position setpoint value to the drive controller. FIG. 1 is a block diagram of a conventional drive controller for an axis. The deviation of the actual position value xact from the setpoint position value xnom is forwarded to a position controller, which forms a speed or rotational speed setpoint value wnom, by multiplying the deviation with an amplification factor Kv. The speed setpoint value wnom is processed in speed controller 2. The output of speed controller 2 is forwarded as current setpoint value Ignom to a current controller 3, via which motor 4 of the axis is ultimately actuated. Current actual value Iquact, speed actual value wact, and position actual value xact are used in a conventional manner for closing the cascading control circuits.
In order to allow a more rapid response to changes in the position setpoint value, a feedforward control unit 1 implements a feedforward control of the rotational speed (or speed) and current, while bypassing the individual controller. In this context, differentiators D are used to determine the first and second derivation of position setpoint value xnom, which are forwarded, as vnom and anom, respectively, to speed controller 2 and current controller 3.
Filters v-Flt, I-Flt, U-Flt, FIR with whose aid undesired resonances are able to be damped, may be acting at quite different locations in the drive controller.
As illustrated, a control circuit is adjustable via numerous parameters. For example, amplification factors Kp, Ki, Kd of the P-, I- and D-components of the different control circuits are stored in the control as machine parameters. The same applies to time constants Tt or the frequency response characteristics of the filters. Machine parameter MP, by which the second derivation of position setpoint value xnom is multiplied prior to being fed forward to current controller 3, is another example of such an adjustable parameter.
All of these settings are undertaken by the manufacturer of a machine tool in order to optimally adapt the numerical control to the machine tool. Parts programs are intended to produce dimensionally correct workpieces with clean surfaces as quickly as possible.